ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT gineering and development section of the Southern Utilination Research Branch for hydrogenating 50 gallons of gum turpentine. literature cited
(1) Feldon, M., technical report AU-936 from Government Laboratories to Office of Synthetic Rubber, 1951. (2) Fisher, G. S., Goldblatt, L. A., Kniel, I., and Snyder, A. D., IND. ENG.CHEM..43. 6714 (1951). (3) Fisher, G. S.,Stinson, j . S., and Goidblatt, L. A., J. Am. Chem. SOC.,75, 3675-8 (1953).
(4) Ipatieff, V. N.,Pines, H., and Savoy, M., Zbid., 69, 1948-52 (1947). (5) Joshel, L.M., Hall, 8. A., and Palkin, S., IND.ENO.CEEM.,ANAL. ED.,13,447 (1941). (6) Kniel, I., private communication from Government Laboratory to Office of Synthetic Rubber, 1950. (7) Lipp, A,,Bet-., 56, 2098-107 (1923). (8) Wheeler, D. H., oil & soap, 9, 89 (1932). RECEIVED for review January 21, 1954.
ACCEPTED February 3, 1956.
Conservation of Butylenes in Butadiene Manufacture C. R. NODDINGS,
S.
B. HEATH, AND J. W. COREY
Dow Chemical Co., Midland, Mich.
D
EVELOPMENT of a suitable catalyst has resulted in the commercial dehydrogenation of n-butenes to 1,a-butadiene. This article describes the history, production and performance, operating problems, testing methods, and economic factors involved in the development and use of a calcium-nickel phosphate catalyst, designated as Type B catalyst. Some of the data have come from the operation of butadiene plants, and some were made available through the Reconstruction Finance Corp. Past difficulties have been minimized in this presentation. Though serious at the time, they have shown the way t o successful operation. There are few operating troubles that have not been solved. History of catalyst development includes pilot plant and trial production runs
The Dow Chemical Co. was interested in synthetic rubber well before the start of World War 11. The main interest was in styrene; however, considerable thought was given to the problems of making synthetic rubber. In April 1941, E. C. Britton, the 1952 President of the AMERICAN CHEMICAL SOCIETY,and A. J. Dietzler of the Organic Research Laboratory of the Dow Chemical Co. invented on paper a selective catalyst for the dehydrogenation of n-butene to 1,a-butadiene. A small amount of the catalyst was made by coprecipitating calcium, nickel, and phosphate radicals in an aqueous medium. The material performed satisfactorily when it was catalyticaily tested. Two years later the details were worked out for the preparation of the present Type B catalyst. This is the original calcium-nickel phosphate promoted with chromic oxide to make the catalyst function better and last longer. Preparation methods were described in the only other article previously published on this subject ( I ) . The article also contained sections concerning definition of terms and scope of the catalyst thst may aid in the understanding of the present article. The first five United States patents on the catalyst were also listed. There has been one more recent patent ( 7 ) , which discusses the materials of construction to be used inside of a commercial Type B catalyst reactor. I n April 1945, the chemical engineering laboratory of Dow started to develop the commercial process for preparing Type B catalyst for butadiene pilot plant work and sale to butadiene producers. Type B catalyst is sold as pellets, a/,s inch in diameter and 8/18 inch long, packed in 400-pound-net-weight steel drums. The selling price has been in the vicinity of $1.50 per pound. The pellets as received are not ready for use until the 2% by weight of graphite pelletizing agent is removed by roasting the catalyst in the presence of steam and air. July 1355
Pilot plant work was carried out in 1945 using a small ethylbenzene dehydrogenation furnace located at Sarnia, Canada. Full scale operation was first observed in 1946, also at Sarnia, but was not successful. Two more trial runs were made in 1950, a t Sarnia, with fair success. These operations have been described in detail by Reilly (9). Reilly (9) also revealed that Polymer Corp., Ltd., first used this catalyst for successful commercial operation on July 24, 1951. Six-foot beds were used in two of the four Jersey-type design adiabatic reactors. Success in the other two reactors was achieved on September 11, 1951. Since then, all of Polymer Corp.’s butadiene has been made over Type B catalyst. At Baytown, Tes., the Humble Oil and Refining Co.-operated RFC plant has been 5oY0commercially on Type €3 catalyst since June 25, 1952. These facilities are similar to those of the Polymer Corp. Humble made one early experimental run using a %foot bed of catalyst; later commercial runs have used 6-foot beds. At Borger, Tex., the Phillips Chemical Co.-operated RFC plant has been experimenting since August 16, 1951, with Type B catalyst on a relatively smaller scale, in one of their four isothermal butadiene production units. Production and performance evaluations are made from commercial production of butadiene
The three operators have produced (as of May 18, 1953) approximately 93,000 short tons of butadiene using Type B catalyst. This production figure is based on the following starting dates-Polymer Corp., July 24,1951; Humble, June 25,1952; and Phillips, August 16, 1951. Catalyst consumption has been 500 tons, of which an estimated 185 tons was still in use, with an average of 42% useful life remaining, in May of 1953. Assumptions were 1 week turn around time between runs, 7 months of catalyst life, and 9501, recovery of butadiene made in the reactor. About 220 tons of butadiene was recovered each day using the 185 tons of catalyst. This 220 tons is equivalent tb 15y0 of the rated capacity of all petroleum butadiene plants of the RFC ( 8 ) . (Most of the petroleum butadiene is made in Canada.) The 220-ton production has been made by ten different runs; six have been completed for an average of 7.0 months of actual on-stream usage. Of the ten, the six runs reflecting the best operating techniques were on stream an average of 99.2% of the time, as of May 18, 1953, not including the time between runs. Of the four runs remaining, two were current runs for which the data were not known. The other two were completed runs that had long periods of down time due to fires or mechanical failures that were not directly connected with catalyst operational problems.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1373
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
THIS IS THE STORY of Dow’s Type B catalyst
. . .amoted calcium-nickel phosphate prowith chromic oxide . . .for dehydrogenating n-butene to 1,&butadiene
The shortest run was 5.9 months on stream. The longest standard run was 7.6 months. There was a special run that was 9.2 months in duration. It has a steam heat treatment rejuvenation (patent applied for) at 4 months of age. A typical catalyst life story is shown by Table I. This is a composite of commercial results and represents wHat should happen month by month when no attempt is made to keep the catalyst from wearing out prematurely. A 2-hour cycle is used when on stream; 1 hour of this is the process period during which a mixture of n-butene and steam is passed over the catalyst. The other hour is used for valve changing and the regeneration period when an air plus steam mixture is passed over the catalyst. The data are for two 6-foot beds, 970 cubic feet of catalyst each, or 57.5 to 60 tons of Type B catalyst. Process flows at 60” F., 1 atmosphere, perfect gas, per (volume of catalyst) (hour) are 118 volumes of n-butene and 2500 volumes of steam. Regeneration flows are 125 volumes of air and 770 volumes of steam. These “constants” vary about &5%.
Table 1.
5
6
7
Temperature, F. Mixed AF feed 48 1115 1150 52 1163 51 1173 47 1178 42 1182 49 Rises a t 1184 end of run
con-
seieoversion tivity, Mole % Mole % 29 90 32 91 35 91 36 90 36 90 35 89 34 88
.
Several possible reasons have been found for premature aging of Type B catalyst. Copper Poisoning. Recycle unreacted butene from cuprous ammonium acetate extraction systems deposits copper on the top of the bed for a downflow Jersey reactor. In 7 months this deposition has been as high as 400 p.p.m. copper in the catalyst pellets. New catalyst contains 20 t o 30 p.p.m. of copper. Most of the copper, which is a known poison to Type B catalyst, is in the top third of the bed. How much such molecularly deposited copper can be tolerated is not known.
Production, Tons/Day ButaCardiene bonyls 52 2.5 58 2.7 60 2.6 62 2.4 61 2.1 61 1.8 58 ?
The variables listed in Table I are primarily connected with the mixed feed temperature of n-butene and steam. This temperature must be continually raised, but more slowly as time goes by, to maintain an interesting conversion level of n-butene to other chemicals. The efficiency of this conversion, as far as butadiene is concerned, is called selectivity. The tabulated data all are for the dehydrogenation reactors only, since there is some loss of product during extraction and purification, and they are based on materials balances rather than carbon balances. The carbonyl by-product ( 4 ) is acetone with some methyl ethyl ketone’and methyl vinyl ketone, along with many minor chemicals. It was calculated as acetone. The carbonyl concentration in the dilute butadiene reactor product shows a linear drop off with time so that after 6 months the concentration is half what it was after the first month of operation. Carbonyls are, a t present, extracted with water and thrown away. They do, however, offer a source of revenue equivalent to 2 or 3’% selectivity. The AF equals maximum catalyst temperature on regeneration minus the mixed feed temperature used during the preceding reaction or process period. The AF is used to measure the sensitivity of the catalyst. Ordinary troubles, such as raising the conversion level too high, are spotted when the AF increases
1374
Extension of catalyst life i s one of current use problems
Typical Month-by-Month Life Story for Type B Catalyst in a Jersey Dehydrogenation Unit
opera-
tion, Months 1 2 3 4
each cycle, There is time to correct the trouble before permanent damage is done. The rapid increase of AF a t the end of the run results from catalyst “exhaustion,” even though operating conditions may have been held constant during the preceding month. When the AF increases at this time, large amounts of carbon are laid down in the catalyst bed, and there is no other recourse but to terminate the run. This is called a premature failure since all of the uncoked catalyst, except a shallow layer a t the top of the bed, is good, high selectivity catalyst. The top of the bed is lower in selectivity and does not contain any carbon. Since nothing has been found in the coked catalyst, and it can be made to perform satisfactorily after removal of the accumulated carbon, there is every reason to believe it was also high selectivity catalyst to the time of the carbon deposition.
Figure 1.
Type B catalyst performance versus oxidation-reduction state Low activity catalysl
Chromic Oxide Loss. Recycle hydrocarbon from butyl rubber plants contains organic chlorides in a parts per million concentration range. The reaction products with the chromic oxide are slowly carried away, mostly from the top third of the bed. As much as half of the original 2y0 by weight of chromic oxide has been lost in 3 months. Usually, about one third is lost in 6 to 7 months of operation. How much loss can be toferated is not known, and adding fresh chromic oxide to the used catalyst does not have any effect on catalyst quality.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7 ‘
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT Table II.
Possible Economic Debits and Credits to Type B Catalyst
Item n-Butene used/ton 1 3-butadiene 1 3-Butadiene/day f;om altered plant to get all units balanced Bk-product isobutanes and butanes By-product carbonyls By-product acetylenes (methyl-, ethyl-, rinyl-) By-product light fuel gases Regeneration air Dehydrogenation. unit steam 37% conversion Miscellaneous chemicals Acetone in feed meparation Lean oil in fractionation H&&, NaOH, NHa,,Cu, acetic acid, flux oil, etc. Hydrocarbon compression power Hydrocarbon refrigeration Recycle 1,3-butadiene degradation Catalyst first expense Catalyst life
Table 111.
+-
Credit = Debit =
++ + Not known -
-
+ ++ Not known ++ + -
Not known
Sintering. Natural loss of surface area as a result of high temperature over a long period of time may influence the ultimate practical catalyst life. Roasted new Type B catalyst pellets have 5 to 6 square meters of surface area per gram determined by nitrogen adsorption a t - 195" C.). This area drops gradually to 2 square meters per gram in 7 months of use. Butene adsorption studies and catalytic tests, however, have shown that nitrogen surface area is not directly related to Type B catalyst activity. In general, though, the lower the nitrogen surface area the less is the catalyst activity. The adsorption of n-butene appears to be the better method of correlating surface area to catalyst activity. Oxidation-Reduction Out of Balance Theory. Figure 1 is a semiquantitative picture of low activity Type B catalytic behavior a t all stages between extreme reduction and oxidation of the catalyst. It is hoped that the abscissa will some day be made
Calculation of Cost of Butadiene Production VARIABLES
Term
Value Used in Example A Example B
Units
A
Selectivity
Moles 1,3-CaHa made Mole n-CaHa reacted
B
Recovery
Lb. 98Yo 1,3-C4H6 recovered for sale Lb. 1,3-C4Ha made
C
n-Butene cost
D
90
90
95
9.5
Cents/lb. 100% n-C4Hs
4a
4"
Steam ratio
Moles steam on reaction Mole n-C4H6 fed
21.2
18
E
Yield
Moles 1,3-C4H6made Mole n-CdHs fed
30.6
30
F
Superheated steam cost
Dollars/1000 lb. steam
0.70a
0.70"
G
Catalyst volume
Cu. f t . catalyst/reactor
970
970
H
Space velocity (gas vol. a t 60' F., 1 atm.)
c u . f t . n-C4H8 fed (Cu. f t . catalyst)(hr.)
118
153
I
Reaction time for two reactors
Reactor hr. Stream day
24
24
J
Regeneration steam
Lb. steam/hr.
35,500
35, 500b
K
Regeneration reactors
Regeneration hr. Stream day
24
24
L
Catalyst weight for two reactors
Lb. catalyst
117,500
117,500
M
Catalyst cost
Dollars/lb. catalyst
1.50
1.50
N
Run length
Months of run
9.48
9.45
time
for
two
loo = %
loo =
x
100
=
%
%
Months on stream P On-stream time 0.966 Month of run Values arbitrarily chosen in order to illustrate equations. b Value a t a minimum when = 5500dlb./sq. inch gage, superheated steam pressure a t furnace in range of 25 to 45 lb./sq. inch gage.
0.966
COSTCALCULATIONS
Eguation
I
Item n-Butene
56,lIb. n-C4Hs (54.1 lb. l,?,-C4H6)(?)(?)'')
+ o'02(c)
I1 Reaction steam (superheated) I11 Production of one dehydro unit of two reactors '
5 4 , l Ib. 1,3-C&a (379 cu. f t . n-CaHe a t 60° F. and 1 atm.)
IV
1 (J)(short tons l,3-CaHe /stream day, from Equation
V
VI
Regeneration steam (superheated) Catalyst
Fixed items
(L)(M)(w) (h) ($)( ) (e)
B
E
100 cents) ( K ) ( short ton)
dollar
(lo)*, where z =
4.55
- 2.41 X
4.93
1.70
1.48
57'0a
72'4'
0.52
0.41
0.55
0.44
4.07
3.95 11.21
10-6 (short tons 1,3-CaHe/stream day, from Equa-
(w) year (P)
Total Short tons of 98% butadiene per stream day.
July 1955
2000 Ib.
1 (short tons 1,3-C&Ts/stream day, from Equation I11 short ton 1 3 - C 4 H ~ months on stream 2000 lb. l,;-CaH6 ( 3 0 . 5 stream days
tion III) a
short ton 1,3-C4H6
( 2000 lb. 1,3-C& ) (1ooo/,) ( ~ ) ( G ) ( H ) ( r )
4.93
INDUSTRIAL AND ENGINEERING CHEMISTRY
11.77
1375
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT quantitative. Empirical methods of comparison among samples for relative positioning were used in building the graph of Figure
The first fivejequations are straightforward and can be used for any n-butene to butadiene catalyst a t any values of the variables involved. Equation V I is based on United States government data. It holds true only for the 1953 price level of labor, supplies, chemicals other than catalyst, utilities other than superheated steam, overhead, etc. The accuracy of Equation VI is f0.5 cent per pound of butadiene. Cost items not accounted for in Equation VI are depreciation, research, sales and administrative charges, and United States income tax. Equation VI applies to petroleum butadiene plants producing from 20,000 to 200,000 short tons of butadiene per year a t the rate of 20,000 to 40,000 short tons per year per Jersey dehydrogenation unit or its counterpart based on another design. Two examples are given for the equations. Example A corresponds to operating data presented in this article for Type B catalyst. Example B represents a potential set of conditions for Type B catalyst which illustrates the effect of several changes in the variables. Other Uses. Type B catalyst can be used in other dehydrogenation reactions. When it works, selectivities over 90% have been obtained. Conversion of ethylbenzene to styrene and isopropylbenzene to a-methyl-styrene has already been discussed (1). These are not the only possible reactions, but Type B is used commercially to make only butadiene a t the present time.
1.
Higher activity catalyst, up to 50% 1,3-butadiene (maximum), shows the same selectivity lines shown in Figure 1; but the activity and conversion lines are more or less parallel to those of Figure 1, at least in the central portion of the abscissa. The performance curve for roasted new catalyst starts at the maximum activity point and the activity slowly decreases towards overoxidation during commercial use. Type B catalyst fails in 7 months when the top of the bed is operating within area G. Low selectivity results in more carbon than can be removed during regenerations. The bottom of the bed is only in area F , but it is the place where residual carbon accumulates until the run is stopped. Testing Methods. Figure 1 is based on hundreds of catalytic tests made by the Dow standard test No. 5 (3). Average data a t 650' C. were used. The catalyst samples were new or used catalyst with histories of varying degrees of oxidation or reduction prior t o the test. The standard No. 5 test is useful not only as a control for quality catalyst production, but also as a tool for investigating catalyst peculiarities. It cannot be used to predict Type B catalyst life. An abusive life test is used a t present that synthetically wears out the catalyst within a week or two. It is run a t 500 volumes of n-butene per (volume) (hour) and 700" C. compared to the standard No. 5 test a t 300 volumes per (volume) (hour) and 650' C. (maximum) for only ten 1-hour cycles. Solutions for Use Problems. There are several ways of extending Type B catalyst life. None have been tested sufficiently to enable a prediction of ultimate catalyst life to be made. Copper poisoning and chromic oxide loss could be handled by various methods of feed stock purification or by replacing the affected catalyst periodically. These problems and overoxidation are all affectedbeneficially by a heat treatment rejuvenation with steam. This treatment may be as long as 24 hours of steaming a t 675" C. (1247" F.) every 3 months, for the type of operation shown in Table I. The performance of the catalyst can be returned to area E of Figure 1. Other methods of approaching day to day in balance operations, for Figure 1, will probably be worked out. There may be an optimum pellet size which is larger than a / inch in diameter-say, 7/32 or 1/1 inch. This could permit a butadiene production greater than the present maximum sustained production rate of over 80 tons of butadiene per day from two 6-foot beds. By-products are additional credit source in economy of process
All other catalysts (6, 6, 8, 9) that have ever been used commercially to make butadiene from Ca hydrocarbons operate well under the selectivity level of Type B. The use of Type B catalyst results in many economies in addition to the main one of n-butene conversion. Table I1 lists some of these in a debit and credit manner. All these economies should be considered when cost of using Type B is calculated. The major items affecting the cost of butadiene manufacture can be gathered together in the six equations shown in Table 111.
1376
Conclusion
~ ~
Type B catalyst has been commercially useful to several butadiene manufacturers. To conserve as much n-butene as possible, all butadiene should be made over this catalyst. Since costs of conversion of plant equipment to the use of Type B catalyst are high for plants other than the Jersey process, all possible economies must be considered. Future plants, built as demand for synthetic rubber increases, are likely users of Type B. Existing plants cannot be scrapped because they are slightly obsolete. Thus it becomes important to find ways of obtaining longer Type B catalyst life. If the catalyst lasted 1 t o 2 years, possibly all butadiene plants could afford to convert. Provision of longer catalyst life does not appear to be an insurmountable task nor an uneconomical problem. literature cited
Britton, E. C . , Dietaler, A. J., and Noddings, C. R., IND. ENQ. CREM.,43, 2871-4 (1951). Chem. Eng. News, 31, 1096 (1953). Dow Chemical Co., Midland, Mich., Analytical Method MLE. 051.30. 1951.
Finigan, C. M., Fullerton, H. V., m d Taylor, G. W., IND. ENQ. CHEM.,45, 135E-9 (1953).
Grosse, A. V., Morrell, J. C . , and ;Mavity, J. M., Ibid., 32, 309-11 (1940).
Kearby, K. K., Zbid., 42, 295-300 (1950). Noddings, C. R., Waldron, G. W., and Corey, J. W., U. S. Patent 2,641,619 (June 9, 1953). Reidel, J. C., Oil Gas J . , 51, 82-90 (1953). Reilly, P. M., Chemistry in Can., 5, 41-5 (1953). RECEIVED for review February 3, 1954. ACC~FTED December 8, 1954. Presented as part of the Symposium on Petrochemicals in the Postwar Years before the Division of Petroleum Chemistry at the 124th Meeting of the AMERIC.4N CHEMICAL SOCIETY, Chioapo, 111.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 7
